General aviation pilot reported receiving a low altitude alert from ATC during approach.

Narrative

This was my first flight into ZZZ using the RNAV (GPS) RWY XX approach. As I approached the ZZZZZ waypoint; ATC asked if I would be crossing ZZZZZ at 1;500 feet. I replied that I was following the glideslope but was approximately 400 feet too high. I had misread the altitude depiction on the approach plate; interpreting the bars above and below 1;500 feet incorrectly; which caused me to remain above the proper glideslope.Recognizing the error; I disconnected the autopilot and began an immediate descent. After being switched to tower frequency; I was slightly low and received a low-altitude alert. This occurred because I failed to properly brief and verify the altitude restrictions on the approach.I understand that the specific altitude requirements on this procedure are critical due to proximity to ZZZ traffic. The ATC controller was professional and emphasized the importance of crossing ZZZZZ at the published altitude. No Brasher warning was issued. This event resulted from my misinterpretation of the approach plate and inadequate briefing; and I am submitting this report to document and learn from the error.